1. Field of the Invention
This invention relates generally to an apparatus and method used in connection with monitoring reaction forces such as those associated with the application of tension, traction, or torque. The invention is particularly applicable to the direct measurement of such forces exerted on an infant during delivery.
2. Description of the Related Art
There has never been an easy or practical way to directly measure the forces that are exerted on an infant as he/she is delivered in the birth process. Since, for example, the maternal pelvis can cause some obstruction when the baby is delivered, the obstetrician often has to exert some external force on the infant to complete the delivery. As a baby emerges from the mother""s pelvis, the obstetrician often must pull on the baby""s head to deliver the shoulders and, eventually, the rest of the body. If the shoulders are broad and/or the body is large, a substantial amount of force may be necessary to complete the delivery. If the obstetrician applies too great a force, it is possible to cause injury, such as a tearing of nerves in the baby""s neck or shoulder. Such injuries may result in, i.e., permanent paralysis of part of the shoulder, arm and/or hand. There has been no simple or practical device for monitoring the force applied in delivering an infant, and there have been only scattered attempts to measure, either directly or indirectly, such a force in an experimental situation.
There have been attempts to measure such forces indirectly with special gloves (H. Allen et al., xe2x80x9cRisk Factors for Shoulder Dystocia: An Engineering study of Clinician-Applied Forcesxe2x80x9d, Obstet. Gynecol., 77:352, 1991), a mechanical model (R. H. Allen et al., xe2x80x9cComparing Clinician-Applied Loads for Routine, Difficult, and Shoulder Dystocia Deliveriesxe2x80x9d, Am. J. Obstet. Gynecol, 171:1621, 1994), and a mathematical model (B. Gonik et al., xe2x80x9cMathematic Modeling of Forces Associated with Shoulder Dystocia: A Comparison of Endogenous and Exogenous Sourcesxe2x80x9d, Am. J. Obstet. Gynecol., 182:689, 2000). None of these potential solutions has been widely accepted, primarily because they are not practical or accurate, and have not been able to measure the actual forces that are imposed upon the infant during delivery. The first method above used tactile sensors in gloves worn by the attending obstetrician as the baby was delivered. However, the sensors were not on all fingers, and did not cover the entire hand of the obstetrician. The last two models could only approximate the forces of delivery, and many assumptions were required to be used as the models were created.
Force platforms that measure forces in three orthogonal directions are known, such as shown in U.S. Pat. No. 5,029,483 to Gautschi et al., and U.S. Pat. No. 5,400,661 to Cook et al. However, these platforms and others have been used to measure forces that were applied to the platform for such purposes as analyzing the way a person or animal stands, sways, or walks in controlled situations or in response to specific stimuli. Somewhat similar platforms have been used in sports applications and/or medical applications. Previous platforms have relied on complex sensors that measured three orthogonal forces. Such known sensors were unduly complex.
Availability of a practical delivery monitor would facilitate research to determine how much force is xe2x80x9ctoo muchxe2x80x9d for a safe birth delivery. Accurately measuring the force applied to a baby during delivery will allow studies to be done to determine the types of forces that may safely be applied and threshold(s) at which injuries may occur, and the various factors that might affect these thresholds, e.g. sex, size and estimated weight of the baby prior to birth, the amount of time a particular force is exerted, etc. Such knowledge, if properly put into use by medical practitioners, could protect infants from injury that could otherwise occur.
A conventional way to measure force (weight) is by use of a scale. There are several ways that conventional scales are built. Many are purely mechanical. A modern electronic scale may use, for example, a strain transducer which changes its electrical conductivity or generates a small voltage due to imposed strain or a piezoelectric effect. This can be measured based on the degree to which the transducer is compressed, stretched or stressed. When one side of such a transducer is attached to a stable platform on the bottom of the scale and the other side is attached to a movable top of the scale, force or weight can be measured electronically by measuring a change in, i.e., the conductivity or the voltage produced by the transducer. This measurement is then converted electronically into a readable format (e.g., meter or digital indicator).
However, conventional scales are limited to measuring force only in the direction of the weight of the object due to gravitational pull.
Various tools and specialty instruments are used in industry to measure force, traction, or tension. For example, in the case of torque, many different wrenches or suitable tools are currently available for different sized bolts, screws, or other fasteners. These measure torque directly by determining, in particular devices, how much the wrench bends or flexes as the bolt/screw is tightened. Unfortunately, these specialized tools are usually either expensive or relatively inaccurate due to the difficulty of accurately measuring how much the wrench bends. In any event. Each is normally very highly specialized so as to be applicable for only one or a very limited number of tasks.
What is needed, therefore, is a more reliable, universally applicable, and less costly approach to measuring various forces in three dimensions associated with traction, tension, or torque, whether such forces were applied to an object directly by human touch or through use of intermediate elements such as hand tools. What is even more particularly needed is an apparatus and method for directly and reliably measuring the forces applied to an infant during the birthing process.
The present invention provides an apparatus and method which solves the aforementioned problems associated with measuring forces applied to or exerted on an object by direct human touch or by application of intermediate elements such as tools and other implements. The invention is applicable in a wide variety of situations, For example, the invention is applicable in industrial applications to measure the force or torque that is applied to an object such as a nut or bolt using a tool. The invention is particularly applicable to measurement of the forces applied to a baby during delivery. As discussed above, the apparatus and method of the present invention will facilitate safer births and allow for studies relating to birth trauma, all of which may eventually lead to a decrease or even elimination of some forms of birth trauma.
The present invention also provides a novel force sensor which is particularly suitable for measuring force accurately in a single direction without error introduced as a result of extraneous forces in other directions. One, or more than one such force sensors in combination, is useful in the force measuring apparatus and method of the invention.
It is a fundamental of physics that for every action there is an equal and opposite reaction. The novel method and apparatus for measuring forces in accordance with the present invention does not rely upon measuring the forces where they are applied. Rather, the applied forces are measured at a location where the reaction occurs. Therefore, in accordance with a novel method of the invention, when the obstetrician is pulling on the baby, for example, the applied force is balanced by an equal and opposite reaction force that is applied through the feet of the obstetrician to whatever surface he or she is standing upon. Measurement of the reaction force will provide an accurate and reliable measurement of the force actually applied to the infant.
Similar situations and applications of the present invention may occur in industry. When a technician or mechanic is applying torque or adjusting tension/traction of an element, the reaction to this applied force will be balanced by an equal and opposite force applied through his feet onto the surface upon which he is standing. This means that, if a person is pulling or pushing on an object, the pulling or pushing force must be balanced at some point by an equal and opposite reaction force. If the person is standing, then that reaction force will appear at that person""s feet, imposing a force upon the surface on which the person is standing. The apparatus and method of the present invention is adapted to measure these forces.
The apparatus and method of the present invention comprises transducers for measuring forces in three-dimensions as well as associated electronics for calculating in three-dimensions a resultant force vector which represents the force exerted on an object.
Further, an apparatus in accordance with the invention preferably comprises individual force sensors, each for making a measurement in a sole direction. Three such sensors arranged in mutually orthogonal orientations can be used to measure forces in each of three mutually orthogonal directions, thus measuring forces in three dimensions. Each force sensor may comprise elements constrained to move in a linear fashion, i.e., only along a single direction. The simplicity of such sensors allows them to be modular and, advantageously, allows them to be interchangeable, so that an individual platform can be calibrated for virtually any force range.
A preferred form of apparatus according to the invention may include a stable (i.e., immovable) platform, a movable platform, and intervening force sensors. An individual may stand on the movable platform during some procedure or function in order to measure forces applied to some object during the procedure.
An apparatus according to the invention need not be limited to a platform. Any structure or arrangement is suitable so long as it interfaces with and responds to a person performing a procedure, during which a force to be measured is applied, in such a manner as to react freely to the applied forces to provide a measurement of the reactive forces.
An apparatus in accordance with the invention may typically include a display or output device, which may take various forms, for providing to the operator an indication of the magnitude and/or direction of the force(s) being applied. The display or output device may be an alphanumeric display or a meter, some other sort of visual display, a light, or an audio device that emits one or more sounds or tones. Various types of alarms or auxiliary controls are also useful in a combination of elements according to the invention. For example, an alarm may be used to signal that an applied force has reached a level that represents an upper limit that could be applied safely in a certain situation (such as delivering a baby). A fixed output tone could represent a target force level, and a variable output tone could be used which changes with the applied force level. In this manner, the operator could listen to the audible output while concentrating on whatever task was at hand, rather than on a display, thus avoiding distraction.
The apparatus and method of the present invention has applicability a broad variety of situations, and may replace a variety of tools. For example, torque applied to a bolt or other component may be determined by measuring, with an apparatus according to the invention, the perpendicular force (Fp) applied to a lever-arm of known length (L) about an axis of rotation, e.g., a wrench handle, and calculating a torque (T) as the product of the applied perpendicular force (Fp) and lever-arm length, i.e., T=Fpxc3x97L. The present invention will allow the tension, traction, pressure, torque, etc. to be measured in many situations without need for specialized tools previously required.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent.